One of the most entertaining animes I've seen, you can not get bored in each chapter, all is well animated, fights are exciting, the soundtrack is great, it's very, very recommended.
I will not give spoilers because there is not much to say about this series, the name and the opening say it all.
What it is interesting are the characters who have a history of his past that does not reveal the series yet, for that time the manga
This series is to enjoy the fights and great animation, the story is simple itself. And I do not say that is the best anime in the world because he had put 10, but no; because it is not anything special.